1. Field of the Invention
This invention relates to an optical fiber ferrule retainer used to retain an optical fiber ferrule at a predetermined position in front of an object lens when the shape, etc., of the tip part of the optical fiber ferrule forming a part of an optical connector is analyzed using a microinterferometer (also called “interference microscope”), for example.
2. Description of the Related Art
An optical fiber used for optical communications is made up of a core having an outer diameter of about 10 μm, for example, and a clad layer having an outer diameter of about 125 μm, for example, provided on the outer periphery of the core. An optical connector is installed at a connection end part to connect optical fibers.
The optical connector includes an optical fiber ferrule (simply, called ferrule) for retaining and fixing the end part of the optical fiber. The ferrule is implemented as a cylindrical part for retaining and fixing the end part of the optical fiber and the end part of the optical fiber is inserted into a through hole in the center and is fixed with an adhesive, etc., and then the tip end face is polished like a mirror surface. The tip end faces of two ferrules are abutted against each other with the optical connectors, whereby the two optical fibers retained on the ferrules of the optical connectors are optically connected.
As the tip end face of the ferrule, the tip end face polished to a flat face orthogonal to the optical axis and the tip end face polished to a flat face oblique to the optical axis are known. Recently, attention has been focused on an art of applying PC (physical contact) polishing to the tip end face for shaping the tip end face like a spherical surface so as to enhance the intimate contact property between the ferrule tip end faces as the tip end faces become elastically deformed by the press force when the tip end faces of the ferrules are abutted against each other.
By the way, to decrease the light loss accompanying connection of optical fibers by optical connectors, various specifications of high accuracy are defined for the ferrule according to JIS; for the ferrule subjected to the PC polishing, μm-order specifications of six items such as the dimension error of the curvature radius of the tip end face and the misregistration error between the apex of the spherical tip end face of the ferrule and the center of the core of the optical fiber (outer shape center of fiber).
A microinterferometer may be used to examine whether or not the manufactured ferrule matches the specifications. The microinterferometer observes an interference pattern provided by causing an object beam carrying phase information of the surface shape, refractive index profile, etc., of a minute specimen and reference light to interfere with each other and measures and analyzes the shape and change of the interference pattern, thereby providing the phase information of the specimen.
To examine the manufactured ferrule using such a microinterferometer, a ferrule retainer becomes necessary for retaining the ferrule to be examined with high position accuracy at a predetermined position ahead of and opposed to an object lens of the microinterferometer. Hitherto, a device described in JP-A-2005-69697 has been known as such a ferrule retainer:
The ferrule retainer in the related art described in JP-A-2005-69697 has a structure as illustrated in FIG. 7. FIG. 7 shows only the main body portion of a ferrule retainer 500 for retaining a ferrule 10 at a predetermined position in front of an object lens unit of a microinterferometer positioned on the left of FIG. 7.
The ferrule 10 forms a part of an optical connector and usually is housed in a plug of the optical connector. The ferrule 10 retains one end part of an optical fiber (not shown) of single mode type at the center of the outer diameter of a ferrule main body 11, and a holder 12 for housing the ferrule 10 in the plug of the optical connector is attached to the ferrule main body 11. The ferrule main body 11 is made of zirconia ceramic and has a tip end face subjected to PC polishing like a convex so as to easily come in intimate contact with the tip end face of a mated ferrule not shown.
The ferrule retainer 500 in the related art includes a base part 510 made of a circular plate-like member and the base part 510 has a notch 550 extending in an up and down direction and is divided partially into two portions opposed to each other with the notch 550 between, namely, a support portion 560 and a displacement portion 570. The support portion 560 includes a ferrule insertion hole 561 as a through hole extending in an axial direction in the center of the base part 510. The ferrule insertion hole 561 has an inner diameter of roughly the same dimension as the outer diameter of the ferrule 10, and the support portion 560 is adapted to support the ferrule 10 inserted into the ferrule insertion hole 561 on the inner face of the ferrule insertion hole 561.
The displacement portion 570 swings and is displaced with the thin portion of the lower part as a pivotal support point so that the gap of an opening end part (upper end part in the figure) of the notch 550 is expanded or shrunken, and has a press part 571 for retaining the ferrule 10 by pressing the tip part of the ferrule 10 with the displacement on the extension of the ferrule insertion hole 561. Although a mechanism for adjusting the displacement of the displacement portion 570 is not shown, a tip screw part of a displacement adjustment part (not shown) installed in the base part 510 is screwed into a screw hole 572 made in the tip part of the displacement portion 570 and when the displacement portion 570 is pulled into the support portion 560 by rotation operation of the displacement adjustment part, the press part 571 presses the peripheral surface of the ferrule 10 for retaining the ferrule 10.
However, the described ferrule retainer 500 involves the following problem: In the ferrule retainer 500 in the related art, an abrasion occurs in abrasion parts A and B in the ferrule insertion hole 561 and the press part 571 with repetitive retention operation of the ferrule 10, resulting in degradation of the retention accuracy of the ferrule 10.
That is, since the clearance between the inner face of the ferrule insertion hole 561 of the support portion 560 and the outer face of the ferrule 10 is set small so that the center positions match with accuracy, when the ferrule 10 is inserted into the ferrule insertion hole 561, the abrasion part A of the opening end part of the ferrule insertion hole 561 rubs against the outer face of the ferrule 10 and an abrasion occurs.
In the press part 571 of the displacement portion 570, when the displacement portion 570 is bent and is deformed so as to narrow the notch 550 for retention operation by fastening operation of an operation member, the abrasion part B of the inner face of the press part 571 is pressed against the peripheral surface of the ferrule 10 and rubs and an abrasion occurs.
If the retention accuracy of the ferrule 10 is degraded because of occurrence of an abrasion as mentioned above, finally it becomes necessary to replace the whole of the ferrule retainer 500 and arise in the inspection cost is incurred; this is a problem. Particularly, the measurement accuracy of end face inspection of the optical fiber ferrule using a microinterferometer is high, the component dimension accuracy required for the ferrule retainer as a measured article retention component is also high, the cost is increased with greater sophistication of working accuracy, material, working treatment, etc., and the inspection amount also grows with an increase in the use amount of optical fibers; it is importance to solve these problems.
It is therefore a first object of the invention to provide an optical fiber ferrule retainer capable of coping with an abrasion accompanying repeated use to maintain retention of a ferrule forming a part of an optical connector with high accuracy at a low cost.
The ferrule retainer 500 in the related art described above also involves the following problem: In the ferrule retainer 500 in the related art, the displacement portion 570 swings and is displaced with the thin portion of the lower part as a pivotal support point, the press part 571 presses the tip portion of the ferrule 10 for retaining the ferrule 10 and thus the optical axis of the tip part of the ferrule 10 is displaced so that it falls, the retention accuracy is degraded, and an error of the measurement accuracy grows, affecting the analysis result.
That is, the press part 571 is not displaced in parallel with the center line of the ferrule insertion hole with deformation of the displacement portion 570 and is displaced so that the press face is inclined with the center line, and the optical axis of the tip end face of the ferrule 10 is displaced so that it falls because of the effect of the press force. Consequently, the direction of the tip end face changes and the fiber positioned at the center of the ferrule 10 deviates from the center position of the ferrule tip end face to measure, affecting the analysis result.
An abrasion occurs in the ferrule insertion hole 561 and the press part 571 with repetitive retention operation of the ferrule 10, resulting in degradation of the retention accuracy of the ferrule 10; this is also a problem. That is, when the ferrule 10 is inserted into the ferrule insertion hole 561, they rub against each other and an abrasion occurs and an abrasion may occur in the press part 571 with press pressure in retaining the ferrule 10.
It is therefore a second object of the invention to provide an optical fiber ferrule retainer for pressing and retaining a ferrule forming a part of an optical connector with high accuracy without fall displacement of the optical axis of the tip part.